Pd Substitution Research Articles

Catalytic Reduction of Nitroarenes by Dipalladium Complexes: Synergistic Effect

The direct reaction between 2,7-bis(2-pyridinyl)-1,8-naphthyridine (bpnp) and Pd(CH3COO)2 in CF3COOH yields the new dinuclear palladium(II) complex [Pd2(bpnp)(μ-OH)(CF3CO2)2](CF3CO2) (1). Similarly, substitution of Pd(CH3CN)4(BF4)2 with bpnp in DMF gives [Pd2(bpnp)(μ-OH)(DMF)2](BF4)3 (2). Treatment of 1 or 2 with Cl– readily provide the chloro-substituted species [Pd(bpnp)(μ-OH)(Cl)2]+. All complexes were characterized by spectroscopic methods, and the structure of 2 was further confirmed by X-ray crystallography. Complex 1 is an efficient catalyst for the reduction of aromatic nitro compounds leading to the corresponding aniline derivatives under atmospheric pressure of hydrogen at 50 °C. The mechanistic pathway of the catalysis is investigated. From the reaction pathway, it is suggested that a facile condensation of nitroso and hydroxylamine intermediates is enabled by the dipalladium system and the desired transformation proceeds smoothly under mild reaction conditions to yield the reduced product.

Charge density wave quantum critical point with strong enhancement of superconductivity

An experimental study of the rare-earth intermetallic system LuPt2In reveals a strong enhancement of superconductivity near the charge density wave quantum critical point. This represents an unusual counter-example to cuprates, in which superconductivity and charge density waves tend to compete. Quantum critical points (QCPs), at which a second-order phase transition is continuously suppressed to zero temperature, are currently one of the central topics in solid-state physics1,2. The strong interest emerges from observations of very unusual properties at QCPs such as the onset of unconventional superconductivity (SC)3. While QCPs found at the disappearance of magnetic order are quite common and intensively studied, a QCP that results from a structural transition is scarce and poorly investigated. Here, we report on the observation of a charge density wave (CDW) type of structural ordering in LuPt2In with a second-order transition at TCDW = 490 K. Substituting Pd for Pt suppresses TCDW continuously towards T = 0, leading to a QCP at 58% Pd substitution. We find a strong enhancement of bulk SC just at the QCP, pointing to a new type of interaction between CDW and SC.

Palladium-based ferroelectrics and multiferroics: Theory and experiment

Palladium normally does not easily substitute for Ti or Zr in perovskite oxides. Moreover, Pd is not normally magnetic (but becomes ferromagnetic under applied uniaxial stress or electric fields). Despite these two great obstacles, we have succeeded in fabricating lead zirconate titanate with 30% Pd substitution. For 20:80 Zr:Ti, the ceramics are generally single-phase perovskites (g99%) but sometimes exhibit 1% PdO, which is magnetic at room temperature. The resulting material is multiferroic (ferroelectric-ferromagnetic) at room temperature. The processing is slightly unusual (g8 h in high-energy ball-milling in Zr balls), and the density functional theory provided shows that it occurs because of $\mathrm{P}{\mathrm{d}}^{+4}$ in the oversized $\mathrm{P}{\mathrm{b}}^{+2}$ site; if all $\mathrm{P}{\mathrm{d}}^{+4}$ were to go into the $\mathrm{T}{\mathrm{i}}^{+4}$ perovskite B site, only a small moment of 0.1 Bohr magnetons would result.

Critical temperature and upper critical field of Li2Pd3−xCuxB (x=0.0, 0.1, 0.2) superconductors

We studied the effects of substitution of Pd by Cu on the upper critical field of the noncentrosymmetric superconductor Li2Pd3−xCuxB, with x=0.0, 0.1 and 0.2. The upper critical field as a function of temperature was determined by resistance measurements at different magnetic fields. We found that the superconducting transition temperature decreases as the Cu content increases. Moreover, the temperature dependence of the upper critical field is linear in the range of the temperature studied and, at low temperature, is enhanced compared with the prediction of the Werthamer-Helfan-Hohenberg theory. This indicates that the breaking of Cooper pairs by spin orbit scattering and Pauli paramagnetism is negligible, and that the upper critical field enhancement is mainly because the electron-phonon coupling and disorder.

Evolution of a magnetic order in the quasi-kagome lattice system CeRh1–xPdxSn (x ≤ 0.75)

The equiatomic compound CeRhSn with a quasi-kagome lattice of Ce atoms displays a non-Fermi liquid behavior at low temperatures. We have studied how the ground state changes with the substitution of Pd for Rh in CeRh1–xPdxSn (0 ≤ x ≤ 0.75) by measuring the specific heat C, magnetic susceptibility χ, and magnetization M. With increasing x, the lattice parameters a and c increase by 1.6%, the paramagnetic Curie temperature in χ(T) changes from –112 K to 16 K, and M(B = 5 T) at T = 1.8 K increases from 0.05μB/Ce to 1.4μB/Ce. A long-range magnetic order manifests in sharp peaks in C at 0.7, 1.0 and 1.5 K for x = 0.4, 0.5 and 0.65, respectively. An antiferromagnetic order for x = 0.75 is indicated by the observations of peaks in both χ(T) and C(T) at around 3.0 K and metamagnetic behavior in M(B) at B = 2 T. Our results point out that the doping of 4d electrons in the non-Fermi liquid system CeRhSn destroys the coherence of the quasi-kagome lattice and weakens the hybridization between the 4f state and conduction bands, leading to the evolution of antiferromagnetic order.

Efficiency of Cu and Pd substitution in Fe-based perovskites to promote N2 formation during NH3 selective catalytic oxidation (NH3-SCO)

Iron-based perovskites, of LaFe1-xB′xO3-δ (B′=Cu, Pd) formula, are proposed as effective materials for the ammonia selective catalytic oxidation to nitrogen (NH3-SCO). Effects on N2 yield, of copper or palladium substitutions in B position, and of perovskite dispersion over Al2O3 support, are reported. Copper and palladium substitution in perovskite lattice significantly promotes the NH3 conversion rate, owing to the outstanding redox capacity displayed by the substituted compositions at low temperature (T<300°C). While N2 yield decreases upon Cu-doping, it retains as high as 80–90% over Pd-containing catalysts. Copper substitution enhances low-temperature oxygen mobility, which is favorable to NH bond fracture of adsorbed −ONH3 species that results in high NO formation. Palladium substitution results in an opposite effect, and high selectivity towards N2 is obtained. Additionally, N2 yield is significantly improved at high temperature, when perovskite active phase is dispersed over Al2O3 support. Combining in-situ DRIFTS and density functional theory (DFT) calculations, NH3-SCO to N2 reaction pathway over Fe-based perovskites is proposed to follow an Eley-Rideal (E-R) mechanism, during which gaseous NH3 reacts with adsorbed −ONH2 species to form surface diazo species (NN). For LaFeO3, the rate-determining step is the −ON2H2 to −ON2H reaction (overcoming an energy barrier of 3.48eV), while for LaFe0.95Pd0.05O3, the rate-determining step is ON bond cleavage (energy barrier of 1.55eV) that explains then higher N2 yield measured for the Pd-containing perovskite catalyst.

Competition between ferromagnetism and frustrated antiferromagnetism in quasi 2D Ce2.15(Pd1−xAgx)1.95In0.9 alloys

Low temperature thermal and magnetic measurements performed on ferro-magneticl (FM) alloys of composition Ce2.15(Pd1−xAgx)1.95In0.9 are presented. Pd substitution by Ag depresses from 4.1 K down to 1.1 K for x = 0.5, which is related to the increase of band electrons, with a critical concentration extrapolated to . The decrease is accompanied by a weakening of the magnetization of the FM phase. At high temperature (T > 30 K) the inverse magnetic susceptibility reveals the presence of robust magnetic moments ( ), whereas the low value of the Curie–Weiss temperature K excludes any relevant effect from Kondo screening. The specific heat jump at decreases accordingly, while an anomaly emerges at a fixed temperature K. This unexpected anomaly does not show any associated sign of magnetism checked by AC-susceptibility measurements. Since the total magnetic entropy (evaluated around ) practically does not change with Ag concentration, the transference of degrees of freedom from the FM component to the non-magnetic T* anomaly is deduced. The origin of this anomaly is attributed to an arising magnetic frustration of the ground state and the consequent entropy bottleneck produced by the divergent increasing of density of excitations at low temperature.

Evolution of magnetic properties in the solid solution [formula omitted

We have investigated the evolution of magnetic properties in pseudo-ternary UCo1−xPdxGe (x=0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 and 0.9) intermetallics by measurements of ac-magnetic susceptibility and dc-magnetization. The measured samples have been prepared by arc-melting and characterized by powder X-ray diffraction and X-ray energy-dispersive electron spectroscopy technique. Rietveld refinements of the X-ray patterns indicate that the pseudo-ternaries crystallize in the orthorhombic TiNiSi-type structure with Pnma space group as the parent UCoGe and UPdGe compounds do. The magnetic measurements reveal that in addition to an increase in 5f-electron localization degree with increasing Pd concentration, an interesting magnetic phase diagram, which is more complex than that expected from the gradual change in magnetic ground state due to the substitution. Three compositional ranges with different magnetic properties have been established; the coexistence of spin-glass and itinerant-electron ferromagnetic orderings for x≤0.3, antiferromagnetic order occurs in the range 0.4≤x≤0.7, and a complex ferromagnetic structure of more localized 5f moments takes place in x≥0.8. The evolution of magnetic ground states in UCo1−xPdxGe is discussed in terms of interplay between cooperative magnetic interactions. We consider also implications of increasing conduction electrons upon the Pd substitution in Ruderman-Kittel-Kasuya-Yosida interactions, which would give rise to the evolution of magnetic properties in UCo1−xPdxGe pseudo-ternaries.

Enhancement of ductility in Fe-Co based alloys by substitution of Pd

We investigated the relationship between the microstructure and mechanical properties of the ternary Co50Fe50−xPdx alloys with different Pd content. Co50Fe45Pd5, Co50Fe40Pd10 and Co50Fe35Pd15 alloys annealed at 873 K were composed of the α’-matrix having a B2 structure with a high degree of order and two kinds of Fe-Co-Pd precipitates with L10 and L12 structures, which formed at the grain boundaries and in the grain interior. The 0.2% proof stress, tensile strength, hardness and elongation were increased by substituting Pd for Fe in Co-Fe-Pd alloy. It is noteworthy that the Co50Fe40Pd10 alloy had a high tensile strength of 1293 MPa and high total elongation of 12% on average. The significant improvement in the ductility of the Co50Fe40Pd10 alloy is attributed to the ductile Fe-Co-Pd phase that precipitates at the grain boundaries and in the α′-grain interior. The ductile precipitates suppressed the intergranular and cleavage fracture. The increase in strength of Co50Fe50−xPdx alloys is likely to come from both the precipitation hardening and the grain refinement of the α′-matrix.

Composition-induced structural instability and strong-coupling superconductivity inAu1−xPdxTe2

The physical properties and structural evolution of the MX$_2$-type solid solution Au$_{1-x}$Pd$_x$Te$_2$ are reported. The end member AuTe$_2$ is a normal metal with a monoclinic distorted CdI$_2$-type structure with preformed Te-Te dimers. A monoclinic--trigonal structural phase transition at a finite temperature occurs upon Pd substitution and is suppressed to zero temperature near $x$ = 0.55, and a superconducting phase with a maximum $T_{\rm c}$ = 4.65 K emerges. A clear indication of strong coupling superconductivity is observed near the composition of the structural instability. The competitive relationship between Te-Te dimers and superconductivity is proposed.

The effect of Pd on martensitic transformation and magnetic properties for Ni50Mn38−xPdxSn12Heusler alloys

In the past decade, Mn rich Ni-Mn based alloys have attained considerable attention due to their abundant physics and potential application as multifunctional materials. In this paper, polycrystalline Ni50Mn38−xPdxSn12 (x = 0, 2, 4, 6) Heusler alloys have been prepared, and the martensitic phase transformation (MPT) together with the shape memory effect and the magnetocaloric effect has been investigated. The experimental result indicates that the MPT evidently shifts to a lower temperature with increase of Pd substitution for Mn atoms, which can be attributed to the weakness of the hybridization between the Ni atom and excess Mn on the Sn site rather than the electron concentration. The physics properties study focused on the sample of Ni50Mn34Pd4Sn12 shows a good two-way shape memory behavior, and the maximum value of strain Δ L/L reaches about 0.13% during the MPT. The small of both entropy change Δ ST and magnetostrain can be ascribed to the inconspicuous influence of magnetic field induced MPT.

Correlation between topological band character and chemical bonding in a Bi14Rh3I9-based family of insulators

Recently the presence of topologically protected edge-states in Bi14Rh3I9 was confirmed by scanning tunnelling microscopy consolidating this compound as a weak 3D topological insulator (TI). Here, we present a density-functional-theory-based study on a family of TIs derived from the Bi14Rh3I9 parent structure via substitution of Ru, Pd, Os, Ir and Pt for Rh. Comparative analysis of the band-structures throughout the entire series is done by means of a unified minimalistic tight-binding model that evinces strong similarity between the quantum-spin-Hall (QSH) layer in Bi14Rh3I9 and graphene in terms of -molecular orbitals. Topologically non-trivial energy gaps are found for the Ir-, Rh-, Pt- and Pd-based systems, whereas the Os- and Ru-systems remain trivial. Furthermore, the energy position of the metal -band centre is identified as the parameter which governs the evolution of the topological character of the band structure through the whole family of TIs. The -band position is shown to correlate with the chemical bonding within the QSH layers, thus revealing how the chemical nature of the constituents affects the topological band character.

Pd site doping effect on superconductivity in Nb2Pd0.76S5

Pd site doping effect on superconductivity was investigated in the quasi–one-dimensional superconductor Nb2(Pd1−xRx)0.76S5 (R=Ir, Ag) by measuring resistivity, magnetic susceptibility and Hall effect. It was found that the superconducting transition temperature is firstly slightly enhanced by partial substitution of Pd with Ir and then it is suppressed gradually as the Ir content increases further. Meanwhile Ag substitution quickly suppresses the system to a non-superconducting ground state. Hall effect measurements indicate the variations of the charge carrier density caused by Ir or Ag doping. The established phase diagram implies that the charge carrier density (or the band filling) could be one of the crucial controlling factors to determine Tc in this system.

Structural and magnetic phase transitions inCeCu6−xTx(T=Ag,Pd)

The structural and the magnetic properties of ${\mathrm{CeCu}}_{6\ensuremath{-}x}{\mathrm{Ag}}_{x}$ $(0\ensuremath{\le}x\ensuremath{\le}0.85)$ and ${\mathrm{CeCu}}_{6\ensuremath{-}x}{\mathrm{Pd}}_{x}$ $(0\ensuremath{\le}x\ensuremath{\le}0.4)$ have been studied using neutron diffraction, resonant ultrasound spectroscopy (RUS), x-ray diffraction measurements, and first principles calculations. The structural and magnetic phase diagrams of ${\mathrm{CeCu}}_{6\ensuremath{-}x}{\mathrm{Ag}}_{x}$ and ${\mathrm{CeCu}}_{6\ensuremath{-}x}{\mathrm{Pd}}_{x}$ as a function of Ag/Pd composition are reported. The end member, ${\mathrm{CeCu}}_{6}$, undergoes a structural phase transition from an orthorhombic $(Pnma)$ to a monoclinic $(P{2}_{1}/c)$ phase at 240 K. In ${\mathrm{CeCu}}_{6\ensuremath{-}x}{\mathrm{Ag}}_{x}$, the structural phase transition temperature $({T}_{s})$ decreases linearly with Ag concentration and extrapolates to zero at ${x}_{S}$ $\ensuremath{\approx}0.1$. The structural transition in ${\mathrm{CeCu}}_{6\ensuremath{-}x}{\mathrm{Pd}}_{x}$ remains unperturbed with Pd substitution within the range of our study. The lattice constant $b$ slightly decreases with Ag/Pd doping, whereas $a$ and $c$ increase with an overall increase in the unit cell volume. Both systems, ${\mathrm{CeCu}}_{6\ensuremath{-}x}{\mathrm{Ag}}_{x}$ and ${\mathrm{CeCu}}_{6\ensuremath{-}x}{\mathrm{Pd}}_{x}$, exhibit a magnetic quantum critical point (QCP), at $x\ensuremath{\approx}0.2$ and $x\ensuremath{\approx}0.05$, respectively. Near the QCP, long range antiferromagnetic ordering takes place at an incommensurate wave vector $({\ensuremath{\delta}}_{1}0$ ${\ensuremath{\delta}}_{2})$, where ${\ensuremath{\delta}}_{1}\ensuremath{\sim}0.62,{\ensuremath{\delta}}_{2}\ensuremath{\sim}0.25,x=0.125$ for ${\mathrm{CeCu}}_{6\ensuremath{-}x}{\mathrm{Pd}}_{x}$ and ${\ensuremath{\delta}}_{1}\ensuremath{\sim}0.64,{\ensuremath{\delta}}_{2}\ensuremath{\sim}0.3,x=0.3$ for ${\mathrm{CeCu}}_{6\ensuremath{-}x}{\mathrm{Ag}}_{x}$. The magnetic structure consists of an amplitude modulation of the Ce moments which are aligned along the $c$ axis of the orthorhombic unit cell.

Effect of aliovalent Pd substitution on multiferroic properties in BiFeO3 nanoparticles

Bi1−xPdxFeO3 (x = 0, 0.005, 0.01, 0.015) nanoparticles were prepared via a sol–gel method. A single-phase rhombohedrally distorted perovskite structure of all the samples was observed from the Rietveld refined X-ray diffraction (XRD) patterns. The magnetization was increased with the increase of Pd concentration, which mainly ascribed to the increased surface-to-volume ratio and structural distortion. The oxygen vacancy concentration was increased with Pd substitution, which is responsible for the increased leakage current. Interestingly, with the increase of Pd content, the optical band gap (Eg) of Bi1−xPdxFeO3 first increased for x = 0.005 and then decreased for x = 0.01 and 0.015, respectively. In order to explain this phenomenon, a phenomenological qualitative model based on the fluctuation of Fe–O–Fe bond angle and the concentration of oxygen vacancy was proposed.

Magnetostrain and magnetocaloric effect by field-induced reverse martensitic transformation for Pd-doped Ni45Co5Mn37In13 Heusler alloy

In the present work, polycrystalline Ni45Co5−xPdxMn37In13 (x = 0, 0.5, 1, and 3) Heusler alloys were prepared. The influences of Pd substitution for Co on crystal structure, martensitic transformation (MT), and magnetic properties have been carefully investigated for these quinary alloys. The structure measurement indicates that every sample possesses L10 martensitic structure at room temperature. With increasing of Pd content, it is found that the MT region shifts towards higher temperature, but the Curie transition region of austenitic state moves to lower temperature. Owing to the fact that the MT gradually approaches Curie point, the magnetization of austenitic phase is significantly decreased, while the one of martensitic phase almost remains unchanged. In addition, the functional properties associated with the field-induced reverse MT have been also studied in Ni45Co5−xPdxMn37In13 (x = 0, 0.5, and 1) alloys. In comparison to quaternary parent alloy, both of enhanced magnetostrain (0.3%) and isothermal entropy change (25 J/kg K) are observed in quinary Ni45Co4.5Pd0.5Mn37In13 alloy under an applied magnetic field up to 3 T. The implication of such results has been discussed in detail.

Effect of Pd Substitution on Phase Formation and Stability in Ti-Zr-Ni Quasicrystalline Alloys

Abstract Pd can be used as an adding element to improve hydrogenation properties of Ti-Zr-Ni quasicrystalline alloys. However, the action mechanism of Pd addition is unclear yet. The effects of Pd substituting Ti and Zr in Ti45Zr38Ni17 and Ti40Zr40Ni20 alloys were studied by means of XRD, TEM and DSC examination. The results show that icosahedral quasicrystal can be formed purely through 4%∼6% Pd substitution for Ti or 4% for Zr in the Ti45Zr38Ni17 alloy, as well as 3%∼4% for Ti or possibly below 3% for Zr in the Ti40Zr40Ni20 alloy. This indicates a higher substitution limit for Ti in order for the heritance of the quasicrystal phase. Two derived quasicrystals Ti39Zr38Ni17Pd6 and Ti36Zr40Ni20Pd4 can be transformed into crystalline phases after annealing at 400 °C, demonstrating their lower thermo-stabilities in comparison to such Ti-Zr-Ni alloys being stable at about 700 °C. Both the replacement tendency and the decrease of the thermostability of quasicrystal phase might be ascribed to appropriate atomic size of Pd.

Superconductivity and role of pnictogen and Fe substitution in 112-LaPdxPn2(Pn=Sb,Bi)

We report on the epitaxial growth of As-free and phase-pure thin films of the 112-pnictide compounds LaPdxPn2 (Pn=Sb,Bi) grown on (100) MgO substrates by molecular beam epitaxy. X-ray diffraction, reflection high-energy electron diffraction, and x-ray photoelectron spectroscopy confirm the HfCuSi2 structure of the material with a peculiar pnictogen square net layer. The superconducting transition temperature Tc varies little with Pd concentration. LaPdxSb2 has a higher Tc (3.2 K) by about 20% compared with LaPdxBi2 (2.7 K). Fe substitution of Pd leads to a rapid decay of superconductivity, suggesting that these superconductors are conventional type II.

Tuning the pressure-induced superconductivity in Pd-substituted CeRhIn5

The effect of substituting Rh in CeRh1−xPdxIn5 with Pd up to x = 0.25 has been studied on single crystals. The crystals have been grown by means of the In self-flux method and characterized by x-ray diffraction and microprobe. The tetragonal HoCoGa5-type of structure and the c/a ratio of the parent compound remains intact by the Pd substitution; the unit cell volume increases by 0.6% with x = 0.25 of Pd. The low-temperature behavior of resistivity was studied also under hydrostatic pressure up to 2.25 GPa. The Pd substitution for Rh affects the magnetic behavior and the maximum value of the superconducting transition temperature measured at pressures above 2 GPa only negligibly. On the other hand, the results provide evidence that superconductivity in CeRh0.75Pd0.25In5 is induced at significantly lower pressures, i.e. the Pd substitution for Rh shifts the CeRh1−xPdxIn5 system closer to coexistence of magnetism and superconductivity at ambient pressure.

The effects of Pd and/or Zr additives on the structures and cyclic stabilities of Mg50Ni50-based electrode alloys

The Mg50Ni50–based ternary and quaternary alloys partially substituted by Pd and/or Zr have been intensively studied on their structures and electrochemical hydrogen storage performances. The Mg45Pd5Ni50 and Mg45Pd5Ni45Zr5 alloys contained both amorphous phase and body-centered cubic phase, differing from most previously studied amorphous Mg50Ni50–based alloys. The detected lattice parameters of nano-crystalline BCC phase in Mg45Pd5Ni50 and Mg45Pd5Ni45Zr5 alloys were 0.2916 nm and 0.2933 nm, respectively. Charge-discharge tests indicated that Pd facilitates lifting the cyclic retention rate in 20 cycles (C20/Cmax) from 13.2% of Mg50Ni50 alloy to 47.3% of Mg45Pd5Ni50 alloy. The partial substitution of Zr for Ni in Mg50Ni50 alloy improved the initial capacity by 12% from that of Mg50Ni50 alloy (445 mAh g−1). Synergetic substitution of Pd and Zr in Mg50Ni50 can greatly inhibit the corrosion of Mg45Pd5Ni45Zr5 alloy. According to XPS study, the Mg, Pd, Ni and Zr on the surface of Mg45Pd5Ni45Zr5 alloy would be oxidized into MgO, PdO2, Ni2O3 and ZrO2 during charge/discharge cycles. They formed a passive composite film and therefore improved the cyclic stability.